Carbon dioxide scrubber for fuel and gas emissions

ABSTRACT

A system and method for controlling carbon dioxide (CO 2 ) emissions emanating from a gas source includes a CO 2  sorbent bed containing a regenerable sorbent. Exhaust gases flow through the CO 2  sorbent bed before being released into the atmosphere. The CO 2  sorbent bed traps CO 2  contained within the exhaust gas to control the amount of CO 2  finally exhausted to the atmosphere. At least two CO 2  sorbent beds are used such that while one is absorbing CO 2  from the gas stream another is being regenerated. The CO 2  sorbent bed is regenerated to release the trapped CO 2  for disposal or use in other processes. The CO 2  sorbent beds are cycled between absorbing CO 2  and regenerating to optimize absorption of CO 2 .

[0001] This application is a continuation in part of currently pendingU.S. patent application Ser. No. 09/640,440 filed on Aug. 17, 2000.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a system for minimizing carbon dioxideemissions from a stationary source, and specifically for minimizingcarbon dioxide emissions emanating from burning fossil fuels orextracting natural gas.

[0003] There is currently a great interest in reducing emissions ofcarbon dioxide (CO₂) gases into the atmosphere. The amount of CO₂ gasemitted into the air is cited as a factor contributing to globalwarming. CO₂ gas is emitted whenever fossil fuels are burned, such as inautomobile engines and coal burning furnaces used by power plants forthe generation of power. Reductions in the amount of CO₂ gases emittedby such processes is of increased importance and is a point of specificemphasis for government regulatory agencies. This is especially so forpower plants burning large volumes of fossil fuels, emitting largequantities of CO₂ into the atmosphere.

[0004] Currently systems for controlling and eliminating the CO₂ from abreathable air supply are utilized in submarines, space vehicles andspace suits. These systems utilize a CO₂ sorbent bed composed of aplurality of amine sorbent beads disposed within a container. A streamof air containing CO₂ is flowed through the container and the aminesorbent beads. The CO₂ contacting the amine sorbent beads reactstherewith to become trapped within the container. The remainder of thebreathable air recirculates into the controlled environment. Once thecontainer has become saturated with CO₂ such that further absorption ofCO₂ is inefficient, the breathable air stream is switched to a secondcontainer. The saturated container is then exposed to heat or reducedpressure to evolve or release the trapped CO₂ for disposal or use inother systems. Such systems have proven effective and efficient forcontrolling CO₂ content within enclosed environments, however thistechnology has not been applied to environments such as thoseencountered in the operation of a power plant or the extraction ofnatural gas.

[0005] It is therefore desirable to employ technology associated withcontrolling CO₂ in enclosed environments to control exhaust emissionsassociated with burning of fossil fuels and extraction of natural gas.

SUMMARY OF THE INVENTION

[0006] A disclosed embodiment of this invention is a system and methodfor controlling carbon dioxide (CO₂) emissions emanating from a gassource using sorbent beds containing a regenerable sorbent.

[0007] The system controls CO₂ emissions formed from the burning of coalor natural gas by absorbing CO₂ from a gas stream. The system isinstalled such that exhaust gases are communicated through a CO₂ sorbentbed before being released into the atmosphere. The CO₂ sorbent bed trapsCO₂ contained within the exhaust gas such that the now CO₂ minimized gasis finally exhausted to the atmosphere. Another embodiment of thisinvention is installed to control CO₂ content within natural gasextracted from a well. The gas extracted from the natural gas well isrouted through the CO₂ sorbent beds of this invention to control theamount of CO₂ contained within the final product.

[0008] The system includes at least two sorbent beds with one operablyassociated with the exhaust gas stream. The particular sorbent bedcommunicates with the exhaust gas stream by way of an inlet conduit andinlet valve. The inlet valve directs the exhaust gas stream through thesorbent bed such that CO₂ is absorbed and trapped. The outlet valvesdirect gas out of the sorbent bed. While one sorbent bed absorbs CO₂,another sorbent bed is being regenerated to release trapped CO₂ into astorage container for disposal or use in other processes.

[0009] Applying heat above a predetermined temperature to releasetrapped CO₂ regenerates the sorbent bed. A vacuum source is in operablecommunication with the regenerating CO₂ sorbent bed to draw the releasedCO₂ out of the sorbent bed. Alternatively, a steam source is introducedthrough a steam inlet valve to heat the sorbent bed and release CO₂.Steam heats the sorbent bed above the predetermined temperature to causethe release of CO₂ from the sorbent bed and concurrently drive the CO₂out through the outlet valve.

[0010] A controller governs actuation of the heat source and of thevacuum source. The controller is also in communication with the inletvalve and the outlet valve to switch which sorbent bed, the gas streamflows. The controller alternates flow of the gas stream between thesorbent beds, such that one of the sorbent beds is always regenerating,while another sorbent bed is in communication with the gas stream.

[0011] A cooler is in operable communication with the sorbent bed thatis currently in communication with the gas stream to regulatetemperatures within the sorbent bed. Absorption of CO₂ generates a greatdeal of heat, and the sorbent bed works most efficiently at coolertemperatures. The cooler is actuated in response to signals from thecontroller to maintain a desired optimal temperature for the sorbentbed.

[0012] The sorbent beds include a regenerable CO₂ sorbent. RegenerableCO₂ sorbents are capable of repeatedly trapping and releasing CO₂ formany cycles and are therefore desirable for CO₂ removal applicationsincluding exhaust gases exhausted from a smoke stack. Preferably, thesorbent is an amine sorbent applied to a support structure to form aplurality of amine sorbent beads. The amine sorbent beads are packedinto each sorbent bed to contact the gas steam.

[0013] In operation, the controller of the system actuates the inlet andoutlet valves to direct the gas stream through at least one of thesorbent beds. The sorbent disposed within the sorbent bed forms a loosemolecular bond with the CO₂ to trap the CO₂ within the sorbent bed. Theremaining gas is directed out of the sorbent bed either to a storagetank or through a smokestack. The controller actuates the cooler togovern the temperature of the sorbent bed in contact with the gas streamto maintain an optimal temperature.

[0014] The CO₂ sorbent bed is placed within the gas stream, for apredetermined duration calculated to optimize CO₂ absorption. Thecontroller will then actuate the inlet and outlet valves to divert thegas steam to another sorbent bed. The CO₂ saturated sorbent bed is thenregenerated in preparation for another absorption cycle.

[0015] The system and method of this invention employs technology forcontrolling CO₂ in enclosed environments to control exhaust emissionsassociated with burning of fossil fuels and with natural gas production.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows:

[0017]FIG. 1 is a schematic drawing of a system installed to a powerplant producing CO₂ by burning fossil fuels.

[0018]FIG. 2, is a schematic drawing of sorbent beads within a sorbentbed; and

[0019]FIG. 3 is a schematic drawing of another embodiment of the systeminstalled to a well extracting natural gas containing CO₂.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] Referring to FIG. 1, a disclosed embodiment of this invention isa system and method for controlling carbon dioxide (CO₂) emissions froma gas source. The system 10 is schematically shown in FIG. 1 installedto control CO₂ emissions formed from the burning of coal or natural gasby a power plants to generate electrical energy. The waste gasesproduced from burning of coal or natural gas are directed through anexhaust stack and then out to the atmosphere. The system 10 is installedsuch that exhaust gases, indicated at 18, are communicated through a CO₂sorbent bed 20 before being released into the atmosphere. The CO₂sorbent bed 20 traps CO₂ contained within the exhaust gas 18 such thatthe now CO₂ minimized gas is finally exhausted to the atmosphere througha conduit 26.

[0021] The system 10 includes at least two sorbent beds 20, 22 with onlyone operably associated with the exhaust gas stream 18 at any one time.The particular sorbent bed 20, 22 communicates with the exhaust gasstream 18 by way of inlet conduit 24 and inlet valve 38. The inlet valve38 directs the exhaust gas stream 18 through the sorbent bed 20 suchthat CO₂ is absorbed and trapped. The outlet valves 40 direct the flowout of the sorbent bed 20 to a second conduit 26 into the atmosphere.

[0022] While one sorbent bed 20 is absorbing CO₂ , a second sorbent bed22 is being regenerated. Regeneration of the sorbent bed releases thetrapped CO₂ into a storage container for disposal or use in otherprocesses. Although two sorbent beds 20, 22 are illustrated, it iswithin the contemplation of this invention to use any number of sorbentbeds 20, 22 as may be required based on the specific application.

[0023] The sorbent bed 22 is regenerated by applying heat by way of aheat source 30.

[0024] The sorbent bed 22 is configured such that trapped CO₂ isreleased above a predetermined temperature. The heat source 30 isschematically illustrated and maybe of any kind known to a workerskilled in the art. The heat source 30 applies heat to the sorbent bed22 to elevate the temperature above the predetermined temperature torelease CO₂. A vacuum source 32 is in operable communication with thesorbent bed 22 to draw the released CO₂ from the sorbent bed 22 out to astorages or distribution source. Regeneration may also be accomplishedthrough the application of reduced pressures, such as the vacuum withoutthe application of heat.

[0025] Alternatively, a steam source 34 is introduced through steaminlet valve 42 to heat the sorbent bed 22 and release CO₂. Steam fromthe steam source 34 heats the sorbent bed 22 above the predeterminedtemperature to cause the release of CO₂ from the sorbent bed 22. Theregeneration method employed may include one or a combination of heat,vacuum and steam. The specific configuration for regeneration of thesorbent beds 20, 22 is adaptable for each specific application.

[0026] A controller 36 governs actuation of the heat source 30 and ofthe vacuum source 32. The controller 36 is also in communication withthe inlet valve 38 and the outlet valve 40 to switch which sorbent bed20, 22 the gas stream 18 flows. The controller 36 alternates flow of thegas stream 18 between the sorbent beds 20, 22 such that one of thesorbent beds 20, 22 is always regenerating, while one of the sorbentbeds 20, 22 is always in communication with the gas stream 18.

[0027] In one embodiment of the system 10, a cooler 28 is in operablecommunication with the sorbent bed 20 that is currently in communicationwith the gas stream 18 to regulate temperatures within the sorbent bed20. Absorption of CO₂ generates a great deal of heat, and the sorbentbed works most efficiently at cooler temperatures. The cooler 28 isactuated in response to signals from the controller to maintain adesired optimal temperature of the sorbent bed 20. The optimaltemperature of the sorbent bed 20 is determined for each specificconfiguration of sorbent bed in relation to differences in size, type ofsorbent, and characteristics of the gas stream 18.

[0028] Referring to FIGS. 1 and 2, preferably, each of the sorbent beds20, 22 includes a regenerable CO₂ sorbent. Regenerable CO₂ sorbents arecapable of repeatedly trapping and releasing CO₂ for many cycles and aretherefore desirable for CO₂ removal applications including exhaust gasesthrough a smoke stack. Preferably, the sorbent is an amine sorbentapplied to a support structure to form a plurality of amine sorbentbeads indicated at 44. The support structure maybe formed from apolymeric material, an activated charcoal material, an alumina material,or any other porous material as is known to a worker knowledgeable inthe art. The amine sorbent beads 44 are packed into each sorbent bed 44to contact the gas steam 18.

[0029] Preferably, the sorbent is composed of predominantly secondaryamines and one or more nitrile functional groups. The preferred sorbentis a reaction product of tetraethylenepentamine (TEPA) and acrylonitrile(AN). The reaction of TEPA with AN converts the primary amines containedin TEPA to secondary amines. The conversion of the primary amines tosecondary amines enhances the CO₂ sorption capacities relative to othersorbents along with reducing amine volatility. One reaction product ofTEPA and AN, referred to as TEPAN is a reaction resulting from thecombination of 1.0 mole of TEPA and 3 moles of AN to form the branchedacrylic form of TEPAN shown below:

[0030] Another reaction product of TEPA and AN results from thecombination of 1.0 mole of TEPA and 2 moles of AN. This reaction formsthe non-branched acrylic form shown below.

[0031] The use of TEPAN is not preferably used for applications weresteam is used to regenerate the sorbent bed. In addition, although, theuse of TEPAN as the sorbent is disclosed, it is within the contemplationof this invention to use other types of sorbents as would be known to apersons skilled in the art. Such a sorbent includes a sorbent known inthe art as a solid weak base ionic exchange resin with preferred aminefunctionality. This type of sorbent includes amines possessingcharacteristics of high CO₂ absorption.

[0032] The particular sorbent composing each of the CO₂ sorbent beds 20,22 is selected with regard to many application specific factors. Thefactors include and are not limited to, the content of the exhaust gasflowing through each of the sorbent beds 20, 22 along with thetemperature of the exhaust gas stream 18. In addition, the type ofregeneration system used will govern which type of sorbent selected fora specific application. For example, a system using a steam source 34requires the use of a different type of sorbent as a sorbent using heatand vacuum to release CO₂ from the sorbent bed 20, 22.

[0033] Referring to FIG. 3, another embodiment of the system 10 is incommunication with a natural gas stream 52 emanating from a natural gaswell 50. The natural gas stream 52 includes a mixture of Methane and CO₂routed through the sorbent bed 20 to remove the CO₂ and forward theremaining gas out to a supply line indicated at 54. The system 10includes at least two sorbent beds 20, 22 that are cycled into and outof the gas stream extracted from the natural gas well 50. This system 10operates much like the embodiment shown in FIG. 1, except that theexhaust gases flowing through the conduit 54 are the end product of theoperation.

[0034] Referring to FIGS. 1 and 3, in operation, the controller 36 ofthe system 10 actuates the inlet valve 38 and the outlet valves 40 todirect the flow of gas 18, 52 through at least one of the sorbent beds20, 22. The sorbent beads 44 disposed within the sorbent bed 20 formloose molecular bonds with the CO₂ , thereby trapping the CO₂.

[0035] The remaining gas is directed out of the sorbent bed 20 either toa storage tank as indicated at 54 in FIG. 3, or through a smoke stack asindicated at 26 in FIG. 1. The controller 36 actuates the cooler 28 togovern the temperature of the sorbent bed 20 in contact with the gasstream 18, 52 to maintain an optimal temperature. Absorbing CO₂generates heat, and the amount of CO₂ absorbed by the CO₂ sorbent bed20, 22 is proportional to the temperature such that the cooler thesorbent bed 20, the more CO₂ that may be absorbed. The CO₂ sorbent bed20 is placed within the gas stream 18, 52 for a predetermine durationcalculated to optimize CO₂ absorption between regeneration cycles. Thecontroller 36 will then actuate the inlet 36 and outlet valves 40 todivert the gas steam 18, 52 to another sorbent bed 20, 22.

[0036] Regeneration of the sorbent bed 20, 22 occurs by the applicationof heat to release the bond with the CO₂. Heat can be applied by a heatsource 30 or by a steam source 34. A vacuum may be applied with anymeans of applying heat to the sorbent bed 20, 22 such that the releasedCO₂ can be drawn from the sorbent bed 22, 20 and routed to a storage ordisposal location. The controller 36 will govern the duration of timethat heat is applied to desorb, or regenerate the sorbent beds 20, 22.The duration of time will depend on application specific factors such asthe amount of sorbent beads 44 and the size of the sorbent beds 20, 22.The releaser of CO₂ prepares the sorbent bed 20, 22 for a subsequentabsorption cycle.

[0037] The foregoing description is exemplary and not just a materialspecification. The invention has been described in an illustrativemanner, and should be understood that the terminology used is intendedto be in the nature of words of description rather than of limitation.Many modifications and variations of the present invention are possiblein light of the above teachings. The preferred embodiments of thisinvention have been disclosed, however, one of ordinary skill in the artwould recognize that certain modifications are within the scope of thisinvention. It is understood that within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed. For that reason the following claims should be studied todetermine the true scope and content of this invention.

What is claimed is:
 1. A system of removing carbon dioxide (CO₂) from agas produced in energy extracting systems comprising; a CO₂ sorbent bedincluding a CO₂ sorbent, a conduit for communicating a source of gascontaining CO₂ with said sorbent bed, a conduit for communicating saidsorbent bed with an outlet, a regeneration device for evolving CO₂ fromsaid CO₂ sorbent bed, and at least one valve disposed to control a flowof said gas into and out of said sorbent bed.
 2. The system of claim 1,wherein said sorbent is an amine/nitrile CO₂ sorbent, wherein a majorportion of the amine portion of said sorbent is formed from secondaryamine groups, and at least one functional nitrile group.
 3. The systemof claim 2, wherein said sorbent includes an amine constituent which iscomposed of at least 60% secondary amine groups, no more than 10%primary amine groups, and no more than 20% tertiary amine groups.
 4. Thesystem of claim 2, wherein there are a plurality of functional nitrilegroups in said sorbent.
 5. The system of claim 1, wherein said sorbentis a solid weak base ionic exchange resin.
 6. The system of claim 1,wherein said sorbent bed includes a plurality of amine sorbent beads,said amine sorbent beads react with said CO₂ to trap said CO₂ withinsaid sorbent bed.
 7. The system of claim 1, including a plurality ofsaid sorbent beds and at least one of said valves operates to switchsaid flow of gas between said plurality of sorbent beds such that uponsaturation of one of said plurality of sorbent beds anothernon-saturated sorbent bed is placed in communication with said flow ofgas.
 8. The system of claim 1, wherein said regenerative device includesa heater to heat said sorbent bed to temperatures sufficient to evolvesaid CO₂.
 9. The system of claim 1, wherein said regenerative deviceincludes a steam source, said steam source emitting steam into saidsorbent bed to drive absorbed CO₂ from said sorbent bed.
 10. The systemof claim 1, wherein said regenerative device includes a vacuum source todraw said evolved CO₂ from said sorbent beds.
 11. The system of claim 1,including a controller to coordinate operation of said regenerativedevice and said at least one valve.
 12. The system of claim 1, whereinsaid gas stream emanates from a natural gas well.
 13. The system ofclaim 1, wherein said gas stream is produced by burning of fossil fuels.14. The system of claim 1, further including a cooling system operablyassociated with said sorbent bed to maintain a predetermined temperaturewithin said sorbent bed during absorption of said CO₂.
 15. The system ofclaim 1, further including a storage tank in operable communication withsaid sorbent bed and controlled by said at least one valve such that CO₂evolved from said sorbent bed is drawn into said storage tank.
 16. Thesystem of claim 1, further including an exhaust conduit operablyassociated with said sorbent bed to carry away evolved CO₂.
 17. A methodfor removing carbon dioxide (CO₂) from a gas containing CO₂ extractedfrom an energy producing system, said method including the steps of: a.communicating a CO₂ sorbent bed with the gas containing CO₂. b.absorbing CO₂ contained within the gas with the sorbent bed; c.concentrating said CO₂ within said sorbent bed, and d. expelling saidCO₂ from said sorbent bed upon reaching a predetermined concentrationlevel of CO₂.
 18. The method of claim 1, further including at least twosorbent beds such that said step (a) is further defined by placing oneof said at least two sorbent beds within the flow of gas until reachingthe predetermined concentration of CO₂.
 19. The method of claim 17,further including the step of switching the flow of gas from one of saidat least two sorbent beds upon one of said at least two sorbent bedsreaches said predetermined concentration of CO₂.
 20. The method of claim18, wherein said step (d) is further defined by expelling CO₂ from saidsorbent bed at the predetermined concentration of CO₂.
 21. The method ofclaim 18, wherein said step (d) is further defined by raising atemperature of said sorbent bed above a predetermined temperature torelease the CO₂ from said sorbent bed.
 22. The method of claim 18,wherein said step (d) is further defined by applying steam at atemperature above a predetermined temperature to release said CO₂ fromsaid sorbent bed.
 23. The method of claim 18, wherein said step (d) isfurther defined by applying a vacuum to draw the expelled CO₂ out of thesorbent bed.
 24. The method of claim 1, wherein said sorbent bedincludes a plurality of amine sorbent beads.
 25. The method of claim 18,further including switching between said at least two sorbent beds at apredetermined time interval determined to optimize concentration of saidCO₂ within said sorbent bed.